1. Field of the Invention
This invention relates generally to video systems, and more particularly, relates to video microscopes for comparing objects or images which can, for example, be used for aligning and locating the kerf between integrated circuit or discrete device chips formed in a silicon wafer.
2. Background of the Prior Art
In the past, fabrication of integrated circuit or discrete device chips from a single semiconductor wafer required the necessary step of separating the integrated circuit chips or, as the case may be, the discrete device chips. This separation step usually was known as a "sink and break" operation. In some cases a slurry saw was used to separate the chips without a sinking operation.
Several types of optical alignment systems are being used for positioning silicon wafers under a high speed diamond saw generally used for scribing circuit wafers. These prior art systems are all derivations of the binocular comparison microscope which was designed to superimpose two nearly identical images in registration for the purpose of examining image differences, if any.
Optical projection rather than viewing systems have been developed to reduce operator fatigue caused by the need to observe the work area through binocular eyepieces for extended periods. It should be observed that optical projection requires large aperture objective lenses, a high intensity light source and a complex arrangement of lenses and a projection screen which usually required a basic redesign of the work unit such as the alignment or processing machine.
There is also a limit to the intensity of visible and accompanying infrared light which can be projected onto work objects such as silicon wafers without risk of modifying their characteristics. Thus, optical projection systems designed for semiconductor wafer alignment usually have to be viewed in subdued light.
Accordingly, a need existed for a simplified object viewing or processing arrangement or a silicon wafer alignment system which provides a bright, sharp image from a comparatively low intensity light source and which can be easily incorporated into a wafer scoring or other micro viewing machine without extensive modifications. A need also existed for a projection system where the reproduced image of the viewed subject could be located to best serve the operator's requirements and where the reproduced image can be repeated at a supervisory position or elsewhere as often as desired.